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Francium
Fr 87

Francium

Francium is a chemical element; it has symbol Fr and atomic number 87. It is extremely radioactive; its most stable isotope, francium-223 (originally called actinium K after the natural decay chain in which it appears), has a half-life of only 22 minutes. Francium was discovered in 1939 by French physicist Marguerite Perey. It is the last element discovered in nature, and is the second-rarest naturally occurring element after astatine. Due to its extreme rarity and short half-life, francium has no commercial applications and is only used for research.

Alkali Metal 420066
Atomic number 87Z
Atomic mass 223u
Valence e⁻ 1
Electron config. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s1
Density
1.87g/cm³
Melting point
27°C
Crustal abundance
1e-18ppm
Annual production
—
Recycling rate
0%(Radioactive element; no recycling stream)

Why This Element

Francium is the most electropositive and reactive element among natural radioisotopes — yet its extreme rarity (one atom present per 10¹⁸ actinium atoms) and short half-lives mean macroscopic samples will never exist. No industrial applications; Fr-223 was briefly used in biomedical research as a tracer.

Applications

Research

Applications in DepthElement & compound uses

Main Uses of the Element

Francium is the heaviest alkali metal and a highly radioactive element with an extremely short half-life. It occurs only as a trace constituent in natural uranium ores, and each laboratory preparation reaches at most the scale of a few billion atoms—far too little to accumulate a weighable lump of metal. Its most stable isotope, francium-223, has a half-life of only about 22 minutes, so it has no industrial or consumer use at all. Today it serves solely as an object of atomic physics and nuclear-structure research, used to measure atomic energy levels and test theoretical models.

Key Compounds and Their Uses

Francium is chemically similar to cesium, but any of its compounds can only be observed fleetingly as traces in the laboratory; no weighable sample has ever been isolated, and none of them has any practical application.

Element History

The last naturally occurring element discovered, and the rarest (less than 30 grams total exist on Earth at any moment from actinium-227 decay). Discovered in 1939 by Marguerite Perey while analyzing actinium's beta decay chain — she detected a previously unknown alpha-emitting daughter nucleus, Fr-223. No stable isotopes; longest-lived Fr-223 has a 22-minute half-life.

Related Elements

Li · Lithium Na · Sodium K · Potassium Rb · Rubidium Cs · Caesium

Frequently Asked QuestionsLong-tail Q&A · data-driven

What is the melting point of Francium?
27 °C
What is the boiling point of Francium?
677 °C
What is the density of Francium?
1.87 g/cm³
What are the atomic number and category of Francium?
87 · Alkali Metal
Which ore is Francium mainly extracted from?
Actinium decay product
What are the main uses of Francium?
Francium is the most electropositive and reactive element among natural radioisotopes — yet its extreme rarity (one atom present per 10¹⁸ actinium atoms) and short half-lives mean macroscopic samples will never exist. No
Who discovered Francium and when?
Marguerite Perey · 1939